This is a broad project designed to study the effects of immune complexes on cellular functions. The primary aim is to form immune complexes containing human IgG or IgM antibodies which will subsequently stimulate lymphocytes to divide or to modulate antibody production. When reproducible models have been established, the role of regulators such as rheumatoid factors, complement components, and immunoconglutinin will then be studied. It is proposed that rheumatoid factors are in fact normal immune regulators.